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Full text of "Masonry mortar."

building illustrated on front coves 
Atlanta University, Atlanta, Georgia 
Lime-Cement Mortar 



ARCHITECTS 

1 \MI - GAMBLE ROGER--, INC. 



BUILDER 
BARGE-THOMPSON COMPANY 



MASONRY 
M O RTAR 




Vely on Lime 
-tested by time 



BULLETIN 321 



PUBLISHED BY 

NATIONAL LIME ASSOCIATION 
WASHINGTON, D.C. 



Copyright 1934 

NATIONAL LIME ASSOCIATION 

Second Edition 



TABLE OF CONTENTS 

Properties of Mortars and order in which they ^rz discussed 



Workability 8 

it 
Vohfl 

nsibittty 

St i ninth 

Ra' Iming 






( h i. n >i i \< I ; ii 1 1 . > ■ . 
New York 

architects: 

1 Wll - VAN All N 

B\ 1I.IU-. K: FRED r. LEI 

Leak-proof masonry laid up 
with 1:3 lime mortar to 
which not more than 4 bags 
of cement were added to each 
cubic yard of mortar. 




MASONRY MORTAR 

DRY WALLS WITH LIME MORTAR 

A WATER-TIGHT masonry wall has a negligible number of un- 
filled joints or open spaces where brick and mortar apparently meet 
but are not attached. The formation of such openings is influenced by 
the properties of the materials used and class of workmanship em- 
ployed. The presence of openings between units and mortar is the primary 
cause of excessive water penetration into the wall. The excess water 
may or may not enter into the interior of a building as a result of this con- 
dition. If it does, the wet interior is a symptom of the condition. Re- 
peated and prolonged efflorescence on the exterior of the wall is another 
symptom. The condition, however, may exist without these symptoms. 
This condition must be prevented if the masonry is to be durable. No 
material, however weather resistant it may be, can endure for many years, 
under conditions of excessive saturation. The most effective method of 
preventing the condition, wet walls, is to lay up the masonry in a mortar 
having properties which will permit the mason to completely fill all joints. 
The mortar should also possess properties which permit formation of max- 
imum extent of bond plus ability to maintain such bond. 

The fact that openings exist is proved by the many instances of leaky 
walls wherein both units and mortars are comparatively impervious. Mor- 
tars of very low porosity are often associated with bad leaks. Water follows 
the path of least resistance, through the openings between the masonry 
materials, not through these materials. 

Water that enters pores and voids of bricks, stones, mortars, etc., 
readily evaporates from the exterior surface. This is a normal condition 
offering no cause for concern. 

The alarming increase in number of leaking buildings during recent 
years led to an extensive program of research at the National Bureau of 
Standards, the Massachusetts Institute of Technology, the Mellon Insti- 
tute of Industrial Research and other recognized institutions. The prob- 
lem has also been intensively studied by leading authorities in Europe, par- 
ticularly in Great Britain and Sweden. The data resulting from these 
various studies have been analyzed and the following discussion prepared 
in an effort to place authoritative information at the disposal of American 
architects, engineers, building officials, builders and others. 

Assuming proper design, adequate inspection during construction and 
good workmanship, the most important factor in obtaining a water-tight 
wall is the selection and use of a mortar properly adapted to the units, 
taking into consideration the nature and severity of exposure. 



MASONRY MORTAR 



Adaptability of Mortars 

To prevent excessive water penetration into a wall, one must use an 
adaptable mortar. This is a mortar that can be expected to adhere 
satisfactorily to all types of building units. 

Lime promotes mortar adaptability and a mortar rich in lime is suit- 
able for all types of units. An adaptable mortar is first of all workable. 
It has bonding power. It is characterized by low volume changes sub- 
sequent to hardening. It has good extensibility, produces good masonry 
strength and has a rate of hardening compatible with modern methods of 
construction. These properties will be discussed in the light of the results 
of research in the masonry field. 

PROPERTIES OF A MORTAR THAT MAKE IT 
ADAPTABLE AND SUITABLE 

1. WORKABILITY 

Until recent years the term, workability, has been poorly understood 
in its application to masonry mortars. Warren E. Emley in Bureau of 
Standards Technologic Paper No. 169 states: 

"The ability to retain water, while the most important, is not the 
only factor governing plasticity." Due to the fact that water retaining 
capacity is the most important factor governing plasticity and further to 
the fact that this property has been found to be always associated with 
plasticity, it may be said that a measure of the water retaining capacity 
of a mortar provides a good index to its plasticity or workability. 

A factor of lesser importance is the bulk density or weight per unit 
volume of the freshly mixed mortar. Still another factor is its "trowel- 
ability" which may be estimated by the difficulty or ease of forcing it into 
the interstices of a brick surface of very rough texture. The three known 
factors that control workability are then: 

1. Water retaining capacity 

2. Bulk density 
and 

3. Good troweling properties 

(A) Water Retaining Capacity 

The method of measuring the water retaining capacity of different mor- 
tars and the enhancement of this property by the substitution of more and 
more lime for portland cement in lime-cement mortar mixtures are dis- 

8 



WORKABILITY 



cussed in a paper, "Rate of Stiffening of Mortars on a Porous Base," 
appearing in the September 10, 1932, issue of Rock Products. These data 
were obtained during the course of an extensive cooperative investigation of 
masonry mortars at the National Bureau of Standards. The index to water 
retaining capacity was taken as the flow of a mortar on a 10-in. flow table 
after it had been subjected to suction on a standard porous base for a 
definite time interval, 1 minute, 2 minutes, etc. The suction was equiva- 
lent to that of a very porous dry -press brick laid dry in the wall. Water 
is the sole lubricating medium in mortar and the more retentive it is of 
water, the more workable is the mortar under practical working condi- 
tions. If the mortar loses water to the brick too rapidly, it stiffens so 
quickly that intimate contact is not made and as a consequence the mor- 
tar adheres to the brick only in spots. In other words the extent of bond 
is poor. If the mortar has high water retaining capacity the extent of 
bond is good. 

Water is transmitted readily through the unbonded areas, i.e., where 
brick and mortar apparen tly meet but are not attached. This was proved 
by actual tests at the National Bureau of Standards. Typical data are 
given in Table 1. 



TABLE 1 

Water Retaining Capacity of Mortars as Related to the 
Water-tightness of Test Walls 



Mortar Composition 

Lime: Portland Cement: Sand 

Proportions by Volume 



Water Retaining Capacity 
(Flow per cent, after suc- 
tion for 1 minute on a 
standard porous base) 



Maximum rates of leakage 
of 8-inch test walls made 
with Dry-Press bricks 
set dry. (Cubic centi- 
meters of water trans- 
mitted through walls per 
min.) 



0.15:1:3 
1:1:6 
2:1:9 
3:1:12 




402 

386 

98 

128 



Figure 1 illustrates what is meant by "mortar pancakes," These fre- 
quently occur with mortars of low water retaining capacity. As is appar- 
ent, the adhesion of the mortar to the bricks was initially very poor. The 
bricks held together for at least 4 weeks but later came apart due to vol- 
ume changes in the mortar occurring subsequent to its hardening. 






MASONRY MORTAR 




Figure i 

A 1:3 Portland cement and sand mortar and porous dry-press bricks set dry. The mortar 

pancake was very dense and had high strength. A wall wherein this condition exists would 

have neither strength nor water-tightness. 

Bricks identical to those in Figure 1 were wetted by complete immer- 
sion in water for 15 minutes and then laid with this same 1:3 portland 
cement mortar in making brick beams for flexure tests. The mortar hav- 
ing low water retaining capacity when remaining on a base that will not 
absorb an appreciable amount of water will undergo segregation and form 
"puddles." The reader can see where puddles were in Figure 2 which is 
typical. The bricks were found to be separated at the end of 3 months 
when the beam was picked up to be tested. Volume changes in the hard- 
ened mortar had again done their work. In Figure 2, practically all of 
the mortar joint is seen attached to the lower brick. There is a very thin 
film (cement particles mostly) over the flat surface of the upper brick. 
Unbonded areas are also seen. The bond was weaker than the mortar, a 
condition characteristic of mortar having poor bonding power. 

It is difficult to get a satisfactory bond with a mortar deficient in water 



10 



WORKABILITY 




W 




Figure 2 

Poor extent of hand. Porous bricks set wet I r$ minutes total immersion in water I u ith a 1:3 

Portland cement and sand mortar. Note depressions in surface of mortar joint (right due 
to puddles being formed by segregation in the mortar before top brick was placed. The bond 
tailed completely weeks after mortar hardened. Failure was caused by volume change^ 
occurred subsequent to hardening of mortar. 

retaining capacity, no matter what the absorption of the brick may be. 
The results obtained with such a mortar and impervious bricks are com- 
parable to those illustrated in Figure 2 and obtained with porous bricks 
that have been thoroughly wetted before laying them. Figure 1 shows 
what a porous brick laid dry with a mortar of low water retaining capacity 
will do. With a brick of medium rate of absorption there is still trouble 
with this kind of mortar. The mortar will tend both to segregate and 
stiffen too rapidly, the more of one than of the other, dependent on the 
absorption rate of the unit and the speed of bricklaying, this type of 
mortar being very "sensitive" to slight variations in the absorption rate 
among bricks of a kind. 

The data in the last column of Table 1 were obtained by tests that were 
extremely severe, far more so than the conditions to which a wall may be 



11 



MASONRY MORTAR 



exposed in the most severe rain storm. The extent of bond obtained with 
the 2 lime : 1 portland cement : 9 sand and the 3 lime : 1 portland cement : 
12 sand mortars in the walls subjected to these severe tests, was complete 
and for all practical considerations the test walls would have been water- 
tight had they been integral parts of an 8-inch wall. Practically all of the 
water that came through the test walls with these mortars, followed 
through along the porous header bricks. Furring would check this in a 
wall. 

(B) Bulk Density 

The bulk density of a mortar is a factor of such minor importance that 
its discussion is not warranted. Since three-quarters of the total volume 
of dry ingredients is sand, there are very strict limitations imposed on any 
effort to make freshly mixed mortar light in weight. 

(C) Troweling Properties 

A mortar has good or poor troweling properties. The data of the last 
column of Table 2 were obtained with very rough textured face bricks set 
wet. It was observed on breaking the test walls after testing them for 
permeability that the non -plastic mortars did not fill the interstices of the 
rough faces and header ends of these bricks. Rather, they tended to 
bridge across these shallow indentations. The course of the water in its 
movement into and through the test wallettes could be traced by the 
stain left by the dye that was in the water and it was noted that water 
moved under the "mortar bridges" and over the bottom of the depressions 
when the bricks were laid in non-plastic mortars. The more workable 
mortars gave very little evidence of this condition. 

TABLE 2 

Average Rates of Water Transmission Obtained with 
Different Mortars and a Rough Surfaced Brick Set Wet 







Average maximum rates 






of water transmission 


Mortar 


Troweling 


through test wallettes. 


Lime: Cement: Sand 


Properties 


Averages for 3 specimens. 


By Volume 




Cubic centimeters per 

minute. 


0.15:1:3 


Very Poor 


226 


1:1:6 


Good 


43 


2:1:9 


Excellent 


40 


3:1:12 


Superior 


26 


1:0:3 


Good 


36 



12 



BONDING POWER 



These data were obtained at the National Bureau of Standards during 
the cooperative study of mortars for unit masonry. 

2. BONDING POWER 

This property is not so intangible as its name implies. A mortar having 
this property really takes hold on a solid surface. If a mortar can't take 
hold, can't attach itself to a building unit under certain conditions, then 
it has no bonding power under those conditions. We may strive to change 
the conditions by wetting the brick, etc. However, it is a nuisance to have 
to do this and moreover we never know when we have done it satisfac- 
torily. 

Strength is only one of the factors determining bonding power of a 
mortar. Often (see Figure 1) it is a factor of small importance. We are 
not concerned so much with what a mortar can be made to do with 
extreme care and careful nursing in a laboratory, as we are with what it 
does do with reasonable care either in a laboratory or in a wall of 
masonry. With extreme care a poorly adaptable mortar of low water 
retaining capacity and high volume changes subsequent to hardening may 
bond well in the sense that it adheres completely to the unit at all points 
of contact. In such a case the section of failure in tension is practically 
always entirely at the plane of contact of brick and mortar and not in the 
mortar itself. In other words, under the most favorable conditions, a 
poorly adaptable mortar will always have a bond strength that is less 
than the tensile strength of the mortar. 

Bonding power involves general adaptability. Bonding power is 
that property of a mortar which gives it a tendency to adhere uni- 
formly and completely at all points of contact where bricks and 
mortar meet, under widely different conditions and with various 
types of units, the intensity of its adhesion being such that the 
tensile strength of bond is either equal to or greater than that of 
the mortar. 

With reference to two mortars, one being a 1 lime: 1 portland cement: 
6 sand and the other a 1 portland cement : 3 sand mortar (proportions by 
volume), conclusion No. 6 of Bureau of Standards Research Paper No. 
290, "Durability and Strength of Bond Between Mortar and Brick," 
reads as follows: "The ratio, strength of bond to tensile strength of mor- 
tar, was greater with the 1:1:6 than with the 1:3 mortar." More 
recent data, published in Bureau of Standards Research Paper No. 683, 
"The Properties of Bricks and Mortars and Their Relation to Bond," 
show conclusively that mortars richer in lime than the 1:1:6 mix have 

13 



BONDING POWER 





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15 



MASONRY MORTAR 



better bonding power than that mortar. As lime, either putty or dry 
hydrate, was substituted more and more for portland cement, the bond- 
ing power was improved. The tensile strengths of mortar specimens were 
not actually measured in these tests. However, the tensile strength of mor- 
tar is approximately proportional to the corresponding compressive and 
transverse strengths which were measured. 

Table 3 contains data typical of those obtained by these tests at the 
Bureau of Standards. The lime-cement mortar mixtures of Table 3 were 
made with one and the same portland cement. The bonding properties 
of the portland cement mortar and of the portland cement mortar with 
the addition of 15 per cent by volume of hydrated lime are given as data 
for the first and last mortars respectively of Table 3. The bricks listed in 
this table are representative of both extreme and intermediate types from 
the standpoint of rate of absorption. 

The higher the values in the last 2 columns of Table 3, the 
greater the bonding power of the mortar. The greater the diver- 
gence among the ratios in these two columns (Table 3) obtained 
with the 4 different bricks with one and the same mortar mixture, 
the poorer the adaptability of that mortar and conversely. 

In an article published in Part II, Vol. 33, 1933 issue of the Proceedings 
of the American Society for Testing Materials, Professor W. C. Voss of 
the Massachusetts Institute of Technology makes the following state- 
ment: 

"The position has been taken that a brick and mortar assemblage 
which will fail 50 per cent or more in the mortar is far superior to one 
which will not, regardless of the actual strength in pounds per 
square inch. Our reason for this is based upon the fact that it is 
more important to insure a 'bond layer* at the brick line, than it is to 
insure no break in the mortar." 
Even this concise statement gives to high strength mortars of poor 
bonding power more than is their due. Note the expression, regardless 
of the actual strength in pounds per square inch and then note 
that the strength of bond in tension of the last mortar of Table 3 was 
0.0001 times 2,185, or 0.2 lbs. per square inch with brick No. 1 (dry- 
press) set dry. Low bond strength obtained with such a strong mortar is 
well illustrated by Figure 1. 

Data similar to those in Table 3, may be derived from the data of Duff 
A. Abrams as given in Table 10 of Bulletin No. 8, Structural Materials 
Research Laboratory, Lewis Institute, Chicago. Mr. Abrams tested the 
bond between concrete and steel by pull-out tests of 1-inch plain steel 



16 



BONDING POWER 



bars imbedded 8 inches in an 8-inch concrete cylinder. In Table 10 of 
his publication he presents the compressive strength of 6 by 12 -inch 
cylinders together with the maximum bond stress. In the group of tests 
given in this Table (10) hydrated lime replaced an equal volume of port- 
land cement ; therefore the quantity of cement decreased with increased 
percentage of lime. The values in Table 4 were computed from his data. 



TABLE 4 

Effect of Hydrated Lime on the Ratio, Maximum 
Bond Stress to Compressive Strength 



Hydrated Lime, 
Per Cent of Cement 
Plus Hydrated Lime 


Maximum Bond Stress (lbs. /in.-) 
Ratio: . . 9V 
Compressive Strength (lbs. /in. 2 ) 


By Volume 


By Weight 


7 days 


28 days 


3 mos. 


1 year 




20 
50 




11.1 
33.4 


0.24 
0.33 

0.31 


0.25 
0.18 
0.23 


0.21 
0.24 
0.31 


0.23 
0.23 
0.26 



These values were obtained with a 1 :5 mix by volume. Lean mixtures 
tend to have low bonding power and it is especially interesting to note a 
tendency for slight improvement in this property with so lean a mix with 
the substitution of lime for cement. 

With reference to reinforced brick masonry, Professor John W. Whitte- 
more makes the following statement in Vol. XXV, Bulletin No. 9, of the 
Virginia Polytechnic Institute: 

1 'Failure of the individual bricks in tension, bending or shear is 
much less likely to occur than is the failure of the mortar joint in 
tension, bending or shear. The adhesive strength of mortar to 
brick is perhaps the governing factor. 11 
On page 47, Vol. Ill, Brick Engineering, Hugo Filippi states: 

"From the general performance of beams and slabs under test, 
however, there is some evidence that the bond value of the mortar 
joint in shear is an important, if not the controlling factor/ 1 
We have seen that to have bonding power, a mortar must have adapt- 
ability. To have adaptability it must have workability. Good bond neces- 
sitates good extent of bond. Good extent of bond under variable condi- 
tions and with different types of units can only be obtained with a mortar 
that is adaptable. 

17 




architects: delaxo and aldrich 



18 



Divinity School— Vai.i 

urn. i n "l 



tight masonry—free from efflorescence 



volume cement and ». Vv , ^Pose 
■ 




gUflflisiTY, New Haven, Connecticut 

BCILT I933 

ytstfli' Mortar composed of two volumes lime, one 
r , , . nine volumes sand. 



GENERAL CONTRACTORS: SPERRY AND TREAT CO. 



19 



MASONRY MORTAR 



3. VOLUME CHANGES 

There has been more confusion in the treatment and consideration of 
this topic than perhaps any other. It must be borne in mind that mortars 
undergo three distinct types of volume changes. These are: 

(A) Compacting on a porous base 

(B) Shrinkage during early hardening 

(C) Volume changes subsequent to hardening 

The first two, (A) and (B) occur but once during the life history of a 
mortar. The third, (C) occurs over and over again. It is a cyclic process, 
the mortar expanding on becoming damp or wetted and shrinking when 
it again dries out. This cyclic process, alternate expansion and contrac- 
tion, continues over a period of years. The first type of volume change, 
(A), cannot take place unless there is contact of the mortar with another 
material, i.e., a porous body. The types (B) and (C) do not require con- 
tact of mortar with a solid object. 

(A) Compacting on a Porous Base 

a. This type of volume change is essentially unidirectional. The dimi- 
nution in volume is caused chiefly by a shortening of one dimension of the 
mortar joint and in a direction perpendicular to the plane of contact of the 
mortar and solid object, such as brick, tile, etc. The shrinkage is in the 
general direction of the course that the water takes in leaving the mortar 
and entering the porous unit. The higher the water retaining capacity 
of the mortar the less is its compacting on a porous base and con- 
versely. 

b. Compacting on a porous base occurs prior to any appreciable 
hardening or cementing action that the mortar undergoes. 

c. It takes place in a very few minutes and is most rapid at the first 
instant of contact. 

d. It is attended by a rapid stiffening of the mortar, a rapid loss of 
workability due to rapid loss of water. This stiffening is not harden- 
ing through cementing action and must not be confused with it. 

e. The rapid stiffening of a mortar due to compacting on a porous base 
renders it impossible to make good contact between the mortar bed and 
the next course of bricks or to slush the mortar in cross joints when shov- 
ing bricks into place. It prevents the mortar in the horizontal bed on a 
course of bricks from slumping into and filling any vertical joints left open 
by the mason. 

f. The unidirectional compacting pulls the mortar away from the bricks 
in the cross joints. The mortar is too stiff to flow under the pressure of 
bricks laid above it to cause any renewal of contact. 

20 



VOLUME CHANGES 



Lime and rich in lime mortars have high water retaining capacity and 
therefore tend to undergo a minimum of compacting when in contact 
with porous building units (see "Rate of Stiffening of Mortars on a 
Porous Base," Rock Products, September 10, 1932 issue). 

(B) Shrinkage During Early Hardening 

a. This type of volume change is omnidirectional. 

b. It attends hardening through cementing action. 

c. It occurs but once during the life history of a mortar. 

d. Its magnitude is diminished when the mortar is in contact with an 
absorbent unit and is greatest when in contact with solids of zero porosity. 

e. A mortar which hardens slowly is more or less plastic when most 
of this type of shrinkage is completed. 

f. Any possible damaging effect of this type of volume change is de- 
pendent as much (and probably more) on the rate of hardening as on 
the magnitude of shrinkage. 

g. Data obtained during an extensive study at the Bureau of Standards 
show conclusively that this type of volume change is not damaging either 
to the mortar or to the bond between the mortar and bricks. This was 
found to be true regardless of the magnitude of the shrinkage of mortar 
during early hardening. Typical data are given in Table 5. Had the 
shrinkage during hardening been damaging, then with mortars relatively 
high in such shrinkage, we would expect that the strength of bond when 



TABLE 5 

Negative Results Obtained in the Study of Any Possible Damaging 
Effect of Shrinkage During Early Hardening 





Shrinkage During 
Early Hardening 
(Initial 48 Hours) 

Per Cent 


Strength 


of Bond in 
Averages 


Tension at 3 months 
of 3 Tests 


Mortar Composition 
Lime: Cement: Sand 


Brick No. 3 


Brick No. 5 


(By Volume) 


With Lugs 
lbs. /in. L> 


Without 

Lugs 
lbs. /in. 2 


With Lugs 

lbs. /in. - 


Without 

Lugs 
lbs. /in. 1 


0:1:3 

0.15:1:3 
1:1:6 
2:1:9 
3:1:12 
1:0:3 


0.21 
0.30 
0.34 
0.44 
0.63 
0.66 


45.8 
51.5 
40.4 
33.4 
17.6 
14.8 


53.4 
61.5 
41.0 
36.2 
19.6 
15.5 


26.4 
51.3 
35.0 
22.0 
17.0 
11.9 


28.0 
48.2 
27.4 
22.5 
13.5 
12.9 



21 



MASONRY MORTAR 




Photo by Arthur C. Haskell 

Detail of brickwork showing condition of brick and mortar after more than 2<o years of 
exposure %n severe New England climate. 
Joseph Peaslee Garrison House, Rock Village, Massachusetts 

BUILT 1675 — PHOTOGRAPHED 1 933 

Lime mortar used, 



22 



VOLUME CHANGES 



metal lugs were embedded in the joints would be very much less than that 
obtained without the lugs and that this difference would increase with 
the magnitude of such shrinkage. This did not happen. The data were 
obtained by bonding together the flat surfaces of two bricks with half- 
inch mortar joints. Three %-inch lugs were embedded in the joints of 
half of the total number of the two brick-mortar specimens. 

In table 5, most of the values obtained with lugs are slightly lower than 
those obtained without lugs but this difference was apparently independ- 
ent of the magnitude of the shrinkage during early hardening. The 
slightly lower values obtained with lugs are explained on the basis of the 
fact that where the metal lugs touched bricks, mortar did not. There was 
slightly less bonded area with the lugs present. 

Bricks 3 and 5 (Table 5) were about as impervious as any that could 
be found, a condition designed to augment the shrinkage during early 
hardening. The bricks were restrained from coming together as the mor- 
tar shrunk, a condition similar to that obtaining in the vertical joints of a 
wall. An intensive study of available information does not reveal any 
authentic data obtained by carefully controlled tests, that is in conflict 
with the conclusion that shrinkage during early hardening does not 
create openings between mortar and bricks. 

(C) Volume Changes Subsequent to Hardening 

a. This type of volume change is characterized by expansion on wetting 
and shrinkage on drying. 

b. It is cyclic and frequently is rapid if the conditions for wetting and 
drying are favorable. 

c. It takes place in rigid mortar that has an elastic limit. 

d. High volume changes subsequent to hardening are characteristic of 
dense mortars of outstanding hydraulic properties. They are lowest for 
straight lime mortars. This type of volume change is reduced as lime is 
substituted more and more for portland cement (Bureau of Standards 
Research Paper No. 321, "Volume Changes in Brick Masonry Materials"). 

The data shown in Table 13 of Bureau of Standards Research Paper 
No. 683, "Properties of Mortars and Bricks and Their Effect on Bond," 
show that when the extent of bond is poor (less than 90 per cent of the 
flatside area of a brick) there is a tendency for it to be destroyed entirely if 
the mortar is one that has high volume changes subsequent to hardening. 

If the extent of bond is complete or nearly so, high volume changes 
in the hardened mortar tend to produce cracks in a direction more or 
less perpendicular to the plane of contact of brick and mortar. These 

23 



MASONRY MORTAR 



cracks may heal slowly when the mortar is wet, but they occur again and 
again and tend to admit an excessive amount of water into the wall and, 
as a consequence, further occurrence of volume changes is accelerated. 

Usually, a mortar having low water retaining capacity is one that also 
undergoes relatively high volume changes subsequent to hardening. This 
is an undesirable combination, for it usually results in a poor extent of 
bond coupled with conditions which tend to completely destroy the bond 
and leave "mortar pancakes" in the wall. 

4. EXTENSIBILITY 

Extensibility is here denned as the maximum linear deformation 



TABLE 6 

Extensibilities and "Factors of Safety" of Mortars, 
Age 3 months — Average of 3 tests 









Factor of 






Maximum 


safety, values 


Mortar Composition 


Extensibility, 


shrinkage 


of second col- 


Lime: Cement: Sand 


inches per 


subsequent 


umn divided 


By Volume 


100 inches 


to hardening 


by the corre- 






inches per 


sponding 






100 inches 


values of the 
third column 


0:1:3 (portland cement No. 1) (a) 


0.026 


0.084 


0.31 


0:1:3 (portland cement No. 2) (b) . . 


0.025 


0.071 


0.35 


0:15:1:3 (portland cement No. 1 and lime 








No. 3) 


0.031 


0.076 


0.41 


1 :1 :6 (portland cement No. 1 and lime No. 1 ) 


0.028 


0.038 


0.74 


2:1:9 (portland cement No. 1 and lime No. 1 ) 


0.030 


0.026 


1.16 


3:1:12 (portland cement No. 1 and lime No. 1 ) 


0.025 


0.010 


2.50 


1:0:3 (lime No. 1) (c) . . 


0.031 


0.007 


4.43 


1:0:3 (lime No. 2) (d) 


0.028 


0.004 


7.00 


1:0:3 (lime No. 3) (e) 


0.022 


0.001 


22.00 


1:0:3 (lime No. 4) (f) 


0.025 
0.023 


0.006 
0.049 


4 20 


1 :1 :6 (portland cement No. 2 and lime No. 1 ) 


0.47 


2 :1 :9 (portland cement No. 2 and lime No. 1 ) 


0.024 


0.027 


0.90 


3:1:12 (portland cement No. 2 and lime No. 1 ) 


0.024 


0.017 


1.41 


1:1:6 (portland cement No. 1 and lime No. 3) 


0.022 


0.037 


0.60 


2:1 :9 (portland cement No. 1 and lime No. 3) 


0.025 


0.019 


1.31 


3:1:12 (portland cement No. 1 and lime No. 3) 


0.024 


0.013 


1.85 



(a) 

(b) 

(c) 
(d) 
(e) 
(f) 



Portland Cement No. 1— Typical Grey Portland Cement meeting A.S.T.M. 

Standard Specifications. 

Portland Cement No. 2— White Portland Cement meeting A.S.T.M. Standard 

Specifications. 

Lime No. 1— Quicklime meeting A.S.T.M. Standard Specifications. 

Lime No. 2— Hydrated Lime meeting A.S.T.M. Standard Specifications. 

Lime No. 3^Hydrated Lime meeting A.S.T.M. Standard Specifications. 

Lime No. 4— Quicklime meeting A.S.T.M. Standard Specifications. 



24 



EXTENSIBILITY 



(stretching) that a hardened mortar may undergo before it fails in ten- 
sion. It is a dimensionless value and may be expressed as inches per inch, 
inches per one hundred inches, etc. It happens that this property does 
not vary a great deal among mortars of different compositions, provided 
that the proportions of cementing materials to sand is 1 to 3 respectively, 
by volume, in all cases. In tests made during the cooperative investiga- 
tion at the Bureau of Standards, the extensibilities of 50 different mortar 
compositions ranged from 0.014 to 0.035 per cent. The bulk of the speci- 
mens tested had extensibilities within the limits, 0.020 to 0.030 inches per 
100 inches. These values were obtained by transverse tests and the exten- 
sibility was computed by dividing the modulus of rupture by the modulus 
of elasticity, it being assumed that failure was in tension, the mortar speci- 
men acting as a beam supported at both ends and loaded in the middle. 

The real significance of the property, extensibility, is its relation to the 
magnitude of volume changes subsequent to hardening. If the hardened 
mortar shrinks 0. 10 of an inch per 100 inches and has an extensibility of 0.02 
of an inch per 100 inches, its "factor of safety" would be 0.02-0.10 or I. 
If the shrinkage of the hardened mortar is 0.01 of an inch and the exten- 
sibility is 0.02 of an inch per 100 inches of mortar, the factor of safety is 
.02-^.01, or 2. The latter condition is surely more desirable than the 
former. 

A factor of safety of 1 or greater (Table 6) is a desirable condition. 
With mortars of values appreciably less than unity there is likely to be 
either cracking open of joints (if the extent of bond is good) or shearing 
loose from the bricks or other units (if the extent of bond is poor). This 
danger is obviated by the use of lime or lime-portland cement mixtures 
that contain enough lime to keep the ratio of extensibility to maximum 
shrinkage of the hardened mortar above unity. Such mortars remain 
bonded to building units for years and few if any shrinkage cracks appear. 
Table 6 contains data typical of those reported by the Bureau of Stan- 
dards in the cooperative mortars and masonry investigation. (National 
Bureau of Standards Research Paper No. 683.) 

5. STRENGTH 

A strong wall is one having integrity, i.e., adhesion of mortar to units 
throughout. "Mortar pancakes" that keep bricks apart and not together 
do not provide a strong wall, be the strength of the mortar what it may. 
A chain is only as strong as its weakest link. As we have seen this weakest 
link is at the plane of contact of bricks and mortar when the latter has 
poor bonding power. All other things being the same, a water-tight wall 
is always stronger than a leaky one. Under normal conditions a water- 

25 



MASONRY MORTAR 



tight wall will satisfactorily meet all ordinary requirements in the matter 
of strength in so far as masonry of the average load bearing type is con- 
cerned. 

The following comments relative to strength of mortar are to be found 
in circular No. 30 of the National Bureau of Standards: 

"This question of the strength of a mortar is apt to be given undue 
weight. Since masonry is assumed to weigh 150 pounds per cubic 
foot, then the compressive load (in pounds per square inch) at the 
bottom of a wall will be Hi times its height in feet. A mortar with 
a compressive strength of 100 pounds per square inch, should, ac- 
cording to this reasoning, be able to carry a wall 100 X \U = 96 
feet high, or about nine stories. The compressive strength of the mor- 
tar is usually measured by crushing 2-inch cubes. For a homogeneous 
material the unit compressive strength varies with the shape of the 
specimen, being dependent upon the ratio between the least hori- 
zontal dimension and the height. In a cube, this ratio is one. A mor- 
tar joint in a wall may possibly be 9 inches wide by 30 feet long by 
Vz inch thick. In this joint the ratio is 9 - Vz = 18. If a mortar has 
a strength of 100 pounds per square inch when tested in the form of 
a cube, it should theoretically have a strength of 1800 pounds per 
square inch when laid up in the wall." 
Much consideration has been given to the compressive strength of brick 






TABLE 7 

(Data typical of those in Table 13, National Bureau of Standards Research Paper No. 683) 

Transverse Tests of Brick Beams (5 bricks, single tier, 4 intervening mortar joints) 

Values are Averages of Three Tests. Beams Aged Three Months. 

Average Modulus of Rupture 



Mortar Composition 

Lime: Cement: Sand 

(By Volume) 


Brick 

No. 1 

Set Wet 


Brick 
No. 2 

Set Wet 


Brick 

No. 3 

Set Dry 


Brick 

No. 4 

Set Wet 


Brick 

No. 5 

Set Dry 


Brick 

No. 6 

Set Wet 


0:1:3 

0.15:1:3 
1:1:6 (Lime No. 1) 
1:1:6 (Lime No. 2) 
2:1:9 (Lime No. 2) 
3:1:12 (Lime No. 1) 
1:0:3 (Lime No. 2) 


lbs. /in. 2 

52.0* 

19.7* 

56.6 

42.9 

45.1 

29.8 

28.5 


lbs. /in. 2 
208.0 
132.3* 
66.8 
47.6 
42.0 
24.2 
32.2 


lbs. /in. 2 
39.4* 
38.8* 
73.5 
68.2 
39.9 
30.4 
39.3 


lbs. /in. - 
100.7 
126.0 
90.5 
88.8 
83.4 
35.0 
26.8 


lbs. /in. 2 
18.2* 

4.1* 
15.8 

6.8 
10.4 
15.2 
13.0 


lbs. /in. - 
0.0* 
149.2* 
104.7 
122.9 
88.7 
42.1 
32.9 



'Poor extent of bond obtained with at least one of the 3 

26 



specimens. 



STRENGTH 




Woman's Ward, Western State Hospital, Fort Steilacoox, Wash. 

architects: heath, gove & bell, mock & morrison. 

Mortar proportions were two volumes lime putty, one volume Portland cement and 

nine volumes sand. 

piers. It is interesting as well as enlightening to consider the results of 
flexural tests. On page 67 of "Impervious Brick Masonry," publication 
by the Alton Brick Co., St. Louis, Mo., the results of some flexural tests 
with two brick-mortar specimens are given. The average modulus of 
rupture was 41.9 lbs. per square inch with portland cement mortar and 
79.7 lbs. per square inch with a 1 lime: 1 portland cement: 6 sand mortar, 
using the same brick (6 per cent total absorption) in both cases. 

A poor bond is not as noticeable in compression as it is in flexural tests. 
There have been far less data obtained by the latter than by the former 
tests. Unfortunately all too many investigators have overlooked the fact 
that a brick pier of relatively enormous compressive strength may also 
be one in which the extent of bond is poor throughout. The same pier 
when subjected to a test for permeability will often leak like a sieve. 

The data of Table 7 are taken from those of Table 13 of National 
Bureau of Standards Research Paper No. 683, "The Properties of Bricks 
and Mortars and Their Relation to Bond." 



27 



MASONRY MORTAR 



The reader may note that widely divergent values were obtained with 
the portland cement and the portland cement plus 0.15 volumes of lime 
mortars. The average modulus of rupture of the beams with the portland 
cement mortar and Brick No. 3 (of very low absorption) was the same as 
that obtained with the lime mortar and this brick. This was due to poor 
extent of bond in the former case. 

Brick No. 5 (practically zero absorption and of a glassy surface) gave 
low bond strength with all mortars. However, with the more workable 
mortars, the extent of bond was good with this brick. 

Some of the individual values obtained with the first two mortars 
(Table 7) were zero, owing to the fact that when the time came for testing 
the beams it was found that these mortars, poorly bonded initially (due to 
segregation in the mortar), had come loose from the bricks during the 
aging period. The same beams were intact during the first 4 weeks, hence 
it is concluded that the bond in these cases was disrupted through the 
relatively high volume changes subsequent to hardening, characteristic 
of these two mortars. The poor extent of bond in Figure 2 is an illustra- 
tion of the functioning of the first mortar of Table 7 in the beam tests. 

Many authorities recommend that porous bricks be wetted to improve 
the extent of bond. In obtaining data of Table 7, the porous bricks, Nos. 
1, 2, 4 and 6 (ranging from medium to high absorption) were all wetted 
by total immersion for 15 minutes just before laying them. The mortars 
of low water retaining capacity tended to se^re^are even though they 
could not lose water through brick suction. High water retaining capacity 
is always essential with all types of units. Moreover, mortars deficient 
in this property are usually characterized by relatively high volume 
changes subsequent to hardening. These two undesirable properties, low 
water retaining capacity and high volume changes subsequent to harden- 
ing, arc usually associated. The same holds for the desirable combina- 
tion, high water retaining capacity and low volume changes subsequent 
to hardening, and this desirable combination does more to promote 

flTJ ,Z* WaH ° f maS ° nry than moTtar stre ^ th P«" ~. This 
InTjt 1 apPre ° ated and thoroughly borne in mind by all who are 

s^ssssr* unit masonry from the standp ° int ° f b ° th strength 

The greater the divergence of the average values of Table 7, with any 

bt'v of thTr" f " tH ; 6 ^^ ° f brick ' the P°°- «• the adapt" 
zero to 208 m -nd conversely. For example, values range from 

and rom 1 " tT^lT "* "* ** St ™* ht P ° rtland cement mortar 
and from 15.2 to 42.1 lbs. per square inch with the 3 lime: 1 portland 



28 



STRENGTH 



cement: 12 sand mix. This checks the data of Table 3 and with a different 
type of test specimen. 

Bricks have received more than their just share of blame for the trouble, 
lack of bond. The fact that today there are more extreme types of build- 
ing units on the market than obtained in times past, renders it all the 
more necessary that only adaptable mortars be used. As we have seen 
from actual data, an adaptable mortar is an important factor in obtaining 
strength of masonry. 




School Board Administration Toweh and Centkal School Building 
Tacoma, Wash. 

architects: heath, gove & bell contractors: f. h. goss construction ( omfani 

Mortar proportions were two volumes lime putty, one volume cement, and nine volumes sand. 

Mortar in excellent condition after more than jo years of weathering. 



29 



MASONRY MORTAR 



6. WEATHER RESISTANCE 

Two factors control the resistance to frost in unit masonry. These are: 

1. The extent to which the wall becomes saturated during its life 
history and, 

2. The frost resistance of the building materials (units and mortar). 

The first of these two factors is much more important than the second. 
A comparatively dry wall is not exposed to weathering from severe cli- 
matic action. Water is the universal solvent and chief weathering agent. 
When water which saturates a wall is repeatedly frozen and thawed the 
masonry is disrupted regardless of the fact that the materials composing 
it may, in themselves, be frost resistant in the usual laboratory tests. The 
extent of bond between units and mortar in such a wall is poor to begin 
with, else the masonry would not be excessively saturated. A poorly dis- 
tributed bond (not complete in extent) soon fails entirely from frost 
action. 

The freezing and thawing of moisture which, under the most severe con- 
ditions, only dampens or partially saturates the wall, does relatively little 
damage. In such a wall, the extent of adhesion between mortar and units is 
good. The bond is therefore relatively durable both because it is uniform 
and complete and because it is subjected to a minimum of exposure. 

It so happens that those mortars which have the best freezing and 
thawing records in laboratory tests are usually associated with leaky 
masonry. The properties that enable them to endure severe freezing and 
thawing in the laboratory are not properties which cause them to bond 
completely and firmly to various types of building units. It also happens 
that those mortars of relatively less resistance to laboratory freezing and 
thawing are usually associated with dry walls. They have properties 
which insure good adhesion at all points throughout the wall. It is more 
important to avoid excessive exposure of a wall than it is to have ma- 
terials that are the most resistant when severely exposed. Immunity from 
the condition, excessive wall saturation, is more essential than the ability 
of the materials composing the wall to endure excessive satura 1 

ssive dampness in itself is damaging both to health and property. 

Lime mortar has an enviable record for resistance to weathering in the 
oldest brick buildings in the history of this country. The walls in these fine 
old buildings seldom if ever became completely saturated. Therefor' 
lime mortar did not decay and fall out. 

Due regard and care should be given to the subjects, design, construe 
tion, workmanship and maintenance. Masonry should not be too freely 



30 



WEATHER RESISTANCE 




Photo by Arthur C. Haskell Courtesy of Pencil Points 

Hollis Hall— Harvard University, Cambridge, Massachusetts 
built i763 — photographed 1 933 
Lime mortar with a record of 170 years of service in a severe climate. 



31 



MASONRY MORTAR 



exposed, walls should be furred, parapet walls should be protected and 
sills, copings, etc., should be properly flashed. However, attention to 
these details alone will not prevent excessive saturation of a wall. 
With these precuations there must be a judicious selection of mortar ma- 
terials on the basis of the results of exhaustive research in the field of mor- 
tar properties. 

Lime and rich in lime mortars attain their full strength at a rate less 
rapid than that of portland cement mortars. Many of the natural cements 
and hydraulic limes also attain their full strength at rates comparable to 
that of lime mortars. To subject specimens of mortars having a relatively 
slow rate of attaining strength to severe laboratory freezing and thawing 
tests at an early age is a procedure that can only add to an accumulation 
of "misinformation" which is of no practical value. The number of cycles 
of freezing and thawing provided for in the usual laboratory procedure 
before specimens have aged a year is more than would be attained, even 
in a leaky wall, in half a century of normal exposure. The proof of this 
statement is found in the many examples of old masonry in both the 
United States and Europe made of materials which of themselves give 
negative results under prescribed laboratory tests, yet these buildings 
stand today in mute testimony of their endurance after centuries of ex- 
posure. 



7. EFFLORESCENCE 

All building materials contain at least some trace of water soluble sub- 
stances that can appear on the exterior wall surface if there is excessive 
saturation of the wall. 

Table 1 of National Bureau of Standards Technologic Paper No. 370, 
"Cause and Prevention of Kiln and Dry -House Scum and of Efflorescence 
on Face-Brick Walls," shows the superiority of lime mortar from the 
standpoint of water soluble salt content. 

Use lime and keep the wall dry. 

J. A. Van der Kloes, in an article, entitled "Influence of the Qaulity of 
Mortar on Masonry," Quarry, 1911, 16, pages 204-7, states that he does 
not "remember ever having seen efflorescence on brickwork set in lime 
mortar of only lime, fat or hydraulic, and sand." 

M. Hasak, in "Was der Baumeister vom Mortel Wissen muss," pages 
67-69, Berlin, 1925, Kakverlag, G. m.b.H., deprecates the use of cement 
mortar on account of its liability to cause efflorescence. 

In the British Building Research Station Special Report No. 18, "The 

32 



RATE OF HARDENING 



Weathering of Natural Building Stones/' by R. J. Schaffer, there is found 
on page 63: "In the experience of the Building Research Station, cement 
mortars are found to be somewhat more liable to cause efflorescence than 
lime mortars, although hydraulic lime mortars are not always entirely 
immune." 

These statements are not opinions. They are founded on facts. More- 
over, the use of rich in lime mortars promotes dry walls and in so doing 
tends to avoid efflorescence. 

8. RATE OF HARDENING 

Some have expressed skepticism about the use of lime or rich in lime 
mortars for the reason that they believe that such mortars harden too 
slowly to meet the needs of modern construction. Let the facts dispel 
such an illusion. 

TABLE 8 

Rates of Hardening of Mortars on an Impervious Base 
as Indicated by Vicat Tests 





Rates of hardening. Averages of 




3 tests. Values obtained with a 


Mortar Composition 


modified vicat apparatus after 


Lime: Portland Cement: Sand 


the mortar had been on an im- 


(Proportions by Volume) 


pervious (steel) base for 2 hours. 




Millimeters penetration in 30 




seconds. 


0:1:3 (portland cement No. 1) 


5.2 


0:1:3 (portland cement No. 2) 


0.8 


1:1:6 (portland cement No. 1, lime No. 1) 


1.8 


2:1:9 (portland cement No. 1, lime No. 1) 


3.8 


3:1:12 (portland cement No. 1, lime No. 1) 


4.0 


1 :1 :6 (portland cement No. 2, lime No. 2) 


1.0 


2:1:9 (portland cement No. 2, lime No. 2) 


2.5 


3:1:12 (portland cement No. 2, lime No. 2) 


3.5 


0.15:1:3 (portland cement No. 2, lime No. 2) 


0.4 


1:1:6 (portland cement No. 1, lime No. 4) 


2.5 


2:1:9 (portland cement No. 1, lime No. 4) 


1.9 


3:1:12 (portland cement No. 1, lime No. 4) 


2.5 


0.15:1:3 (portland cement No. 1, lime No. 4) 


1.8 


1:0:3 (lime No. 1) 


30.0 


1:0:3 (lime No. 2) 


22.7 



Portland Cement No. 1— Typical Gray Portland Cement meeting A.S.T.M. Stand- 
ard Specifications. 

Portland Cement No. 2— White Portland Cement meeting A.S.T.M. Standard 
Specifications. 

Lime No. 1 — Quicklime meeting A.S.T.M. Standard Specifications. 

Lime No. 2 — Hydrated Lime meeting A.S.T.M. Standard Specifications. 

Lime No. 4— Quicklime meeting A.S.T.M. Standard Specifications. 



33 



MASONRY MORTAR 





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34 



MORTAR RECOMMENDATIONS 



Lime mortar containing no cement does harden slowly on an impervious 
building unit. With more porous units such as dry -press bricks there 
should be no difficulty whatsoever. Lime mortar is particularly suitable 
with very porous units set dry in winter construction. The bulk of the 
water is out of the mortar and in the brick before it can be frozen. At the 
same time the lime mortar is sufficiently retentive of water to make the 
necessary intimate contact with the highly porous units without necessi- 
tating wetting such units to any extent whatsoever. Bricks should never 
be wetted when laid in freezing weather. 

Table 8 gives typical data obtained during a cooperative investigation 
as recorded in National Bureau of Standards Research Paper No. 683. 

Complete data covering 50 mortar compositions studied may be ob- 
tained from the National Lime Association, Washington, D.C., on request. 
The higher the value of the second column, Table 8, the more slowly did 
the mortar harden on the impervious base. 

MORTAR RECOMMENDATIONS 

From the foregoing study of essential mortar properties it is apparent 
that lime mortar meets all of the requirements, including strength of 
masonry, for most purposes. 

However, in order to avoid delay, where rapid methods of modern con- 
struction are employed, the addition of portland cement to lime mortar is 
recommended, even though this practice adds to the cost of construction 
and often results in considerable sacrifice in quality of the finished 
masonry. When cement is so added it replaces an equivalent volume of 
lime in the mortar mixture. 

It must be remembered that as portland cement is substituted 
more and more for lime, there is a greater and greater sacrifice of 
the essential properties, water retaining capacity, workability, 
adaptability, bonding power, and low volume changes subsequent 
to hardening. 

Laboratory and service tests have both shown that a mortar consisting 
of two volumes of lime, one volume of portland cement and nine volumes 
of sand is well adapted for use with a wide variety of units and under a 
wide variety of conditions, it is therefore recommended for general use 
where a mortar having a rapid rate of hardening is required. If it is de- 
sired that the mortar strength be increased, it is recommended that the 
sand content be reduced to 7 or 8 volumes but that the ratio, 2 volumes 
of lime to 1 volume of portland cement, be maintained. This procedure 
will increase mortar strength with no sacrifice of the more essential prop- 
erties. 

35 



MASONRY MORTAR 



For walls and piers below grade and for masonry that is continuously 
exposed to wet or damp conditions, a mortar consisting of one volume 
each of lime and portland cement together with six volumes of sand is 
recommended. 

Table 9 is a list of recommended mortar mixes for various types of 
masonry, in different locations and under different loading conditions. 
These data should be useful as a reference in the drafting or revision of 
municipal, state and sectional building codes, and in the preparation of 
specifications for engineering and building construction. 



Famous Old 

Shot Tower, 
Baltimore, Md. 

CONSTRUCTED IN I 847 




Common brick bonded 
with straight lime mortar. 
A fine example of the en- 
during quality of masonry- 
laid up in lime mortar. 



36 



THOMSEN I ELUS CO